permafrost

Permafrost is a compound of permanent (from Latin permanere, to remain through) and frost (Old English forst, from freosan, to freeze). Siemon Muller coined the term in 1943 while working for the US Army's permafrost research program during World War II. The Soviet Union had been studying 'vechnaya merzlota' (eternal frozen earth) since the 1930s, but Muller needed an English equivalent. Permanent + frost: the word was straightforward, accurate, and has remained.

Permafrost underlies about 24% of the Northern Hemisphere's land surface: Siberia, northern Canada, Alaska, Greenland, Tibet. It formed over tens of thousands of years during glacial periods when ground temperatures stayed below freezing continuously. The permafrost layer can be meters to hundreds of meters deep; only the 'active layer' above it thaws seasonally. Everything built on permafrost — pipelines, roads, buildings — depends on the frozen ground as foundation.

The Trans-Alaska Pipeline (1977) was built to accommodate permafrost: where it runs above ground, it sits on special supports that allow heat to dissipate away from the ground, preventing the permafrost from thawing and the pipeline from sinking. Engineers developed refrigerated pilings that actively chill the surrounding soil. Permafrost engineering was a new discipline that the pipeline created.

Climate change is thawing permafrost globally. Thawing permafrost releases methane — a greenhouse gas 80 times more potent than CO2 over 20 years — stored in frozen organic matter accumulated over millennia. Scientists call this the 'permafrost carbon feedback loop': warming thaws permafrost, which releases methane, which accelerates warming, which thaws more permafrost. Muller's 1943 word has become one of the most urgent terms in climate science.